Naphthalene preparation and recovery process



United States Patent 1 3,256,356 NAPHTHALENE PREPARATION AND RECOVERY PROCESS Frank E. James, In, Paris, France, assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana N0 Drawing. Filed Dec. 26, 1961, Ser. No. 162,210 3 Claims. (Cl. 260-672) This invention relates to the conversion of alkyl naphthalenes to naphthalene by the heating at elevated temperatures and pressure of aromatic fractions containing naphthalene boiling above 400 F. in the presence of hydrogen whereby there is produced a mixture of hydrogen, alkanes, low boiling aromatics, naphthalene and aromatics boiling higher than naphthalene. More particularly this invention pertains to the recovery of naphthalene from said reaction mixture.

It has been long known that alkyl naphthalenes when heated with hydrogen at'elevated temperatures in the presence or the absence of catalysts results in the removal of the alkyl groups and the replacement thereof with hydrogen on the ring thus forming unsubstituted naphthalene. The conversion of alkyl naphthalenes to naphthalene by such a reaction may involve hydrocracking or the substitution of hydrogen for the alkyl group substituent on the ring. This hydrodealkylation of alkyl naphthalene has been proposed for the manufacture of naphthalene from aromatic fractions boiling above 400 F. containing alkyl naphthalenes. Such aromatic fractions contain alkyl benzenes, naphthalene benzenes such as tetralins, indanes, etc., dinaphthalene benzenes, a small amount of naphthalene generally less than 5% by volume, C naphthalenes (monomethyl naphthalenes), C naphthalenes (ethylnaphthalenes and dimethylnaphthalenes) and C naphthalenes (ethyl methyl naphthalenes and trimethylnaphthalenes) and are generally derived from petroleum refining streams or fractions thereof high in ethylnaphthalenes especially from the bottom fraction after gasoline-boiling range hydrocarbons have been removed from catalytically reformed naphtha or catalytic reformate.

Catalytic reforming is carried out with a naphtha charge stock having a boiling range of from 100 to 400- 500 F. in the presence of hydrogen and a dehydrocyclization catalyst at 880 to 1000 F. and 50 to 800 pounds per square inch gauge (p.s.i.g.). After reforming, the resulting mixture of hydrocarbons and recycle-hydrogencontaining gas is separated into a liquifiable hydrocarbon gross product and a hydrogen-containing gas for recycle,

generally after cooling the mixture from the reforming operation. The hydrocarbon product contains volatile light ends hydrocarbons, hydrocarbons in the gasolineboiling range (100 F. initial and 350 to 420 F. final boiling pointsin the ASTM distillation) as well as higher boiling materials. After removal and recovery of the gasoline-boiling range hydrocarbons by distillation, there remains the bottoms which are almost entirely aromatics with up to 2 to 5% non-aromatics mainly C to C alkanes and alkenes such as in a mixture having a gravity of 8.5 to 8.7 degrees API. Such a bottoms fraction can be used in a hydrodealkylation process, or the bottoms fraction can be stripped of light ends to provide an aromatics concentrate which is then used in a hydrodealkylation process.

The use of the alkyl naphthalene fractions boiling above 400 F. in the hydrodealkylation processes whether catalytic or non-catalytic produce a gasiform reaction mixture containing unreacted hydrogen, since it is used in excess of the mole equivalents of alkyl groups to be removed, alkanes mainly methane with some ethylene, ethane, and minor amounts of C to C alkanes and alkenes, light aromatics boiling below naphthalene and mainly benzene, naphthalene, and aromatics boiling above naphthalene mainly multi-ring compounds with some unreacted alkyl naphthalenes. The light aromatics fraction can be processed to obtain a highly pure benzene or used as such as a high octane blending component of gasoline. Hence a maximum recovery of the light aromatics fraction is highly desirable. The g'asiform mixture from the hydrodealkylation reaction is cooled to condense the hydrocarbons to a liquid product. To maximize the potential recovery of the light aromatics, the gasiform reactor efiluent is cooled to as low a temperature as possible generally Without substantially decreasing the pressure more than to about 750 p.s.i.g. Thereafter a hydrogen stream containing the alkanes and alkenes is flashed off While reducing the pressure on the condensed hydrocarbons about 15 p.s.i. Naphthalene freezes at 180 F. Cooling the mixture of hydrogen and hydrocarbon in the reactor eflluent below 180 F. results in the solidification of naphthalene and other heavier aromatics and the plugging of heat exchangers used for cooling as well as transfer lines between the coolers and collecting vessels such as those from which said hydrogen stream is removed as well as depositing solid naphthalene and heavier aromatics in the flash vessels. A substantial amount of the light aromatics are flashed off with the hydrogen stream at temperatures above 180 F. To recover these flashed off light aromatics from a hydrogen stream lean therein required the use of large condensers, scrubbers, etc. to handle the large volumes of hydrogen stream. For example, when 32 barrels per. hour of the alkyl naphthalene fraction is fed with 5300 standard cubic feet per hour of a hydrogen rich stream mole percent hydrogen and 15 mole percent alkanes mainly methane) to a hydrodealkylation process, about 5500 standard cubic feet per hour of hydrogen stream would have to be handled to recover the light aromatics. A simple procedural step or combination of steps to prevent carry over of light aromatics and permit cooling of reactor effluent below 180 F. even to as low as 80 F. would provide an extremely advantageous operating technique.

The above problem of cooling the hydrodealkylation reaction eflluent below 180 F. can be readily solved by adding to the reaction efiiuent as it is being cooled and prior to flashing off the hydrogen-alkane-alkene stream, a portion of the light aromatics fraction removed from the hydrogen-free aromatics in the sequence of distillation to recover naphthalene. The amount of light aromatics fraction recycled to the cooling step can be varied. To recycle an amount equal to that mole, that is to double the amount in the reactor eflluent and thereafter, during the separation, split the light aromatics one half to product and one half to recycle would amount, in general, to adding about one part of light aromatics by weight per 7 parts of reactor effluent on a weight basis. More of the light aromatics fraction could be collected for recycle when lining out operations and gradually approaching the lower reaction effluent cooling temperature so that the light aromatics content of the reactor eflluent would ultimately be trippled by adding about 1 part of light aromatics to about 3 parts of reactor eflluent by weight. Thus 'of the light aromatics recovered by distillation onethird would go to product and two-thirds to recycle. As little as about 1 part of light aromatics per 10 parts of reactor effluent will permit cooling of the mixture below 180 F. without naphthalene solidfying. The addition of 1 part of light aromatics fraction for 6 to 7 parts of reactor effluent will permit cooling of the mixture to F. without solidifying naphthalene. Suitable for the purposes of this invention, therefore, is the addition of 1 part of light aromatics fraction per 3 to 10 parts of hydrodealkylation reactor eflluent, and desirably, one for each 4 to 7 parts of reactor effluent when cooling temperatures in the range of 80 to 100 F. are employed. The preferred range is 1 part for each 6 to 7 parts where the resulting mixture is cooled to 90-100 F.

To illustrate the process of this invention there is obtained from a methyl naphthalene fraction (13.9 API) containing about 4 mole percent paraflins and olefins, 13 mole percent benzene and 80 mole percent other aro-' matics subjected to hydrodealkylation with hydrogen in the ratio of about 34 pounds hydrogen per 100 pounds of the methyl naphthalene fraction, a reactor efiluent containing about 60 mole percent hydrogen, 19 mole percent methane, mole percent other paraflins and olefins, 2.4 mole percent benzene, 6.7 mole percent naphthalene and 1.9 mole percent other aromatics. For each 65 parts of the reactor eflluent at 850 p.s.i.g. and 210 F., cooled thereto by heat exchange with feed hydrogen and feedstock methyl aromatics fraction and other cooling, there is added 10 parts of light aromatics fraction containing about '55 mole percent benzene, about 10 mole percent toluene, 29 mole percent aromatics boiling above benzene and toluene and up to naphthalene and about 6 mole percent paraffins and olefins. The resulting mixture is cooled and a hydrogen stream (hydrogen and paraflins mainly methane) is flashed therefrom at a final temperature of 90 to 100 F. The remaining liquid hydrocarbon mixture is distilled to recover first a light aromatic fraction containing about 55 mole percent benzene and 10 mole percent toluene, then a naphthalene fraction of about 98% purity (79.4 C. freezing point) leaving a tar or heavy residue.

Hydrogen (A) Methyl Naphthalene (B) HYDRODEME'I'HYLATION REACTOR Fraction: Reactor Effluent Paraifins and. Olefins t mole 5% Hydrogen Benzene 13 mole 7'0 Methane Other Aromatics Other Paraffins Including Methyl and Olefins Naphthalenes 80 mole f1 Benzene Naphthalene Weight ratio (A) to (B) is 3 to 100 Flash Gas Hydrogen and Methane Liquid Hydrbcar'bons (D) Remaining From Flashing Other Aromatics 1.9 mole I HEAT EXCHANGE Recycle (F) Light Aromatics Fraction.

The foregoing example of the process of this invention is illustrated by the following flow sheet type diagram:

When the above process is carried out without the recycle of the light aromatics fraction cooling of the reactor eflluent to about 180 F. or below or a minimum after flashing off the hydrogen stream results in solidification of naphthalene and plugging of heat exchanger as well as solid deposits in the flash vessel.

What is claimed is:

1. In a process for the preparation and recovery of naphthalene by heating together in a reaction zone (A) an aromatic hydrocarbon fraction having 2 to 5% alkanes and alkenes with the remaining 98 to 95% substantially ,aromatic hydrocarbons having alkyl naphthalenes of 11 to 13 total carbon atoms in admixture with alkyl benzenes, naphthalene benzenes, dina-phthalene benzenes and less than about 5% naphthalene with (B) excess hydrogen at hydrodealkylation conditions of elevated temperature and pressure with a net hydrogen consumption in a mole ratio equivalent to the alkyl groups replaced with hydrogen and wherein said excess of hydrogen is an excess above said net hydrogen consumption whereat from said reaction zone a gasiforrn hydrodealkylation reaction effluent mixture at about said elevated temperature and pressure is obtained having as its components hydrogen, methane and C to C alkane and alkene hydrocarbons, aromatic hydrocarbons boiling at a temperature below naphthalene down to and including benzene, naphthalene and aromatic hydrocarbons boiling at a temperature above naphthalene; flashing hydrogen and methane from said reaction eflluent to leave a cooled and depressurized liquid hydrocarbon residue consisting essentially of aro- 60 mole 19 mole lO rnole 2.4 mole 6.7 mole Reactor Effluent (c) at 850 psig and.

Light Aromatics (EMF) Light Aromatics Fraction Benzene mole it Toluene 10 mole je Other Aromatics up to Naphthalene 29 mole Paraffins and.

Olefins 6 mole 5i,

FRACT IONAL DIST ILLi'lT ION Naphthalene Product 9875 I Tar or Heavy Residue (G) matic hydrocarbons and a small amount of C to C alkanes and alkenes and thereafter distilling said liquid hydrocarbon residue to recover at least a light hydrocarbon fraction consisting of benzene and aromatic hydrocarbons boiling below naphthalene and a naphthalene fraction; the improvement for said flashing step of adding to said hydrodealkylation reaction effiuent mixture being -fiash cooled and depressurized said light aromatic hydrocarbon fraction as recycle in an amount in the range of from one part by weight thereof for each 3 to parts by weight of said reaction efiiuent mixture and carrying out said flash cooling to a final temperature ,in the range of from below 180 F. down to about F. whereat the hydrocarbon residue left is liquid.

2. The process of claim 1 wherein the mixture resulting from combining the hydrodealkylation reaction mixture and the portion of the light aromatic fraction is cooled to a temperature in the range of 80 to 100 F. and the amount of the light aromatic fraction admixed with the hydrodealkylation reaction mixture in the ratio of one part of light aromatic fraction for each 4 to 7 parts of reaction mixture on a weight basis.

3. The process of claim 1 wherein the mixture resulting from combining the hydrodealkylation reaction mixture and the portion of the light aromatic fraction is cooled to to F. and the amount of the light aromatic fraction admixed is one part for each 6.5 parts of hydrodealkylation reaction mixture.

References Cited by the Examiner UNITED STATES PATENTS Praeger 208-101 DELBERT E. GANTZ, Primary Examiner.

A. D. SULLIVAN, Examiner.

I. E. DEMPSEY, C. R. DAVIS, Assistant Examiners. 

1. IN A PROCESS FOR THE PREPARATION AND RECOVERY OF NEPHTHALENE BY HEATING TOGETHER IN A REACTION ZONE (A) AN AROMATIC HYDROCARBON FRACTION HAVING 2 TO 5% ALKANES AND ALKENES WITH THE REMAINING 98 TO 95% SUBSTANTIALLY AROMATIC HYDRROCARBONS HAVING ALKYL NAPHTHALENES OF 11 TO 13 TOTAL CARBON ATOMS IN ADMIXTURE WITH ALKYL BENZENES, NAPHTHALENE BENZENES, DINAPHTHALENE BENZENES AND LESS THAN ABOUT 5% NAPHTHALENE WITH (B) EXCESS HYDROGEN AT HYDRODEALKYLATION CONDITIONS OF ELEVATED TEMPERATURE AND PRESSURE WITH A NET HYDROGEN CONSUMPTION IN A MOLE RATIO EQUIVALENT TO THE ALKYL GROUPS REPLACED WITH HYDROGEN AND WHEREIN SAID EXCESS OF HYDROGEN IS AN EXCESS ABOVE SAID NET HYDROGEN CONSUMPTION WHEREAT FROM SAID REACTION ZONE A GASIFORM HYDRODEALKYLATION REACTION EFFLUENT MIXTURE AT ABOUT SAID ELEVATED TEMPERATURE AND PRESSURE IS OBTAINED HAVING AS ITS COMPONENTS HYDROGEN, METHANE AND C2 TO C5 ALKANE AND ALKENE HYDROCARBONS, AROMATIC HYDROCARBONS BOILING AT A TEMPERATURE BELOW NAPHTHALENE DOWN TO AND INCLUDING BENZENE, NAPHTHALENE AND AROMATIC HYDROCARBONS BOILING AT A TEMPERATURE ABOVE NAPHTHALENE; FLASHING HYDROGEN AND METHANE FROM SAID REACTION EFFLUENT TO LEAVE A COOLED AND DEPRESSURIZED LIQUID HYDROCARBON RESIDUE CONSISTING ESSENTIALLY OF AROMATIC HYDROCARBONS AND A SMALL AMOUNT OF C2 TO C5 ALKANES AND ALKENES AND THEREAFTER DISTILLING SAID LIQUID HYDROCARBON RESIDUE TO RECOVER AT LEAST A LIGHT HYDROCARBON FRACTION CONSISTING OF BENZEN AND AROMATIC HYDROCARBONS BOILING BELOW NAPHTHALENE AND A NAPHTHALENE FRACTION; THE IMPROVEMENT FOR SAID FLASHING STEP OF ADDING TO SAID HYDRODEALKYLATION REACTION EFFLUENT MIXTURE BEING FLASH COOLED AND DEPRESSURIZED SAID LIGHT AROMATIC HYDROCARBON FRACTION AS RECYCLE IN AN AMOUNT IN THE RANGE OF FROM ONE PART BY WEIGHT THEREOF FOR EACH 3 TO 10 PARTS BY WEIGHT OF SAID REACTION EFFLUENT MIXTURE AND CARRYING OUT SAID FLASH COOLING TO A FINAL TEMPERATURE IN THE RANGE OF FROM BELOW 180*F. DOWN TO ABOUT 80*F. WHEREAT THE HYDROCARBON RESIDUE LEFT IS LIQUID. 